Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event

Alexander Shishkin
2014-03-10T09:59:54Z

Dave Hansen <dave.hansen@intel.com> writes:

> On 02/17/2014 06:33 AM, Peter Zijlstra wrote:
>> Then write the PERF_RECORD_DATA structure into the normal ring-buffer
>> location; set data_offset to point to the first page boundary, data_size
>> to 1mb.
>>
>> Then frob things such that perf_mmap_to_page() for the next 1mb of pages
>> points to your buffer pages and wipe the page-table entries.
>
> Wouldn't we have to teach a ton of code how to be IRQ safe for this to
> work? Just step one: how do we go modifying page tables safely from an
> interrupt? mm->page_table_lock is a plain non-irq spinlock.

Yes, this does look more than just tricky even if we move the bulk of
interrupt code to an irq_work. Peter, are you quite sure this is what we
want to do just for exporting trace buffers to userspace?

Regards,
--
Alex